Merge branch 'acquire-buffer' into 'master'

buffer: introduce wlr_buffer_acquire()

See merge request wlroots/wlroots!4916

types/buffer/buffer.c

@@ -52,7 +52,14 @@ void wlr_buffer_drop(struct wlr_buffer *buffer) {
 	buffer_consider_destroy(buffer);
 }
 
+struct wlr_buffer *wlr_buffer_acquire(struct wlr_buffer *buffer) {
+	assert(buffer->n_locks == 0);
+	buffer->n_locks++;
+	return buffer;
+}
+
 struct wlr_buffer *wlr_buffer_lock(struct wlr_buffer *buffer) {
+	assert(buffer->n_locks > 0);
 	buffer->n_locks++;
 	return buffer;
 }

types/buffer/client.c

@@ -127,7 +127,7 @@ struct wlr_client_buffer *wlr_client_buffer_create(struct wlr_buffer *buffer,
 	client_buffer->renderer_destroy.notify = client_buffer_handle_renderer_destroy;
 
 	// Ensure the buffer will be released before being destroyed
-	wlr_buffer_lock(&client_buffer->base);
+	wlr_buffer_acquire(&client_buffer->base);
 	wlr_buffer_drop(&client_buffer->base);
 
 	return client_buffer;

types/buffer/resource.c

@@ -57,5 +57,12 @@ struct wlr_buffer *wlr_buffer_try_from_resource(struct wl_resource *resource) {
 		return NULL;
 	}
 
-	return wlr_buffer_lock(buffer);
+	// If the buffer is released, we want to acquire it. If the buffer is
+	// already acquired (e.g. because it has been attached to another surface),
+	// we want to lock it.
+	if (buffer->n_locks > 0) {
+		return wlr_buffer_lock(buffer);
+	} else {
+		return wlr_buffer_acquire(buffer);
+	}
 }